This invention relates to a system and network for protecting a loudspeaker connected in circuit with an audio power amplifier.
In an audio amplification system, it is necessary, in order to protect the loudspeaker, to avoid having any substantial amount of D.C. applied to the loudspeaker. In some systems this objective has been achieved by supplying the output signal of the audio power amplifier to the loudspeaker via a capacitor having a relatively large capacitance. However, the use of such a capacitor substantially attenuates low frequency signals resulting in poor low frequency response.
In order to avoid this disadvantage of the foregoing system, it is known to employ a current amplifier powered from both positive and negative D.C. sources. In such a system the output terminal of the amplifier can be effectively at ground potential, as far as D.C. is concerned, and the other side of the loudspeaker can be grounded, so there will be no D.C. voltage across the loudspeaker. This achieves the desired objective of eliminating D.C. bias on the loudspeaker and, at the same time, does not affect the frequency response of the system.
However, in the case of the last-mentioned system, if there should be a failure of one of the fuses connected between the power supplies and the amplifier, it is possible for a D.C. voltage sufficiently large to damage the loudspeaker to be applied across the loudspeaker.